AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1055 AM EST FRI JAN 2 2015 .SYNOPSIS...HIGH PRESSURE WILL EXTEND OVER THE AREA TODAY. A WARM FRONT OVER THE GULF COAST WILL MOVE NORTHWARD INTO THE REGION LATE TODAY THROUGH SATURDAY... AS ASSOCIATED LOW PRESSURE TRACKS FROM THE DEEP SOUTH NORTHWARD TO THE GREAT LAKES. A COLD FRONT WILL CROSS THE CAROLINAS FROM THE WEST ON SUNDAY. && .NEAR TERM /TODAY/... AS OF 1055 AM FRIDAY... COMPLICATED SURFACE WEATHER PATTERN ACROSS THE EASTERN U.S. THIS MORNING WITH A WEAK AREA OF LOW PRESSURE ACROSS THE WESTERN GULF OF MEXICO...A STALLED FRONTAL ZONE EXTENDING EAST ACROSS THE NORTHERN GULF OF MEXICO AND THEN OFF THE SOUTHEAST COAST WITH A WEAK SURFACE WAVE OFF THE NORTHEAST FLORIDA COAST. A LEE TROUGH PERSISTS EAST OF THE APPALACHIANS IN THE FOOTHILLS WITH A STRENGTHENING AREA OF HIGH PRESSURE OVER THE EASTERN GREAT LAKES. TODAYS WEATHER WILL FEATURE AN ABUNDANCE OF CLOUDINESS ALTHOUGH RECENT VISIBLE SATELLITE IMAGERY AND SURFACE OBSERVATIONS HAVE INDICATED A FEW BREAKS IN THE OVERCAST ESPECIALLY IN THE LOW/MID CLOUDS. IT SATELLITE IMAGERY NOTES A LARGE AREA OF COLD CLOUD CLOUD TOPS UPSTREAM IN THE TENNESSEE VALLEY AND SOME STANDING WAVE ENHANCEMENT ACROSS THE MID ATLANTIC AND DC AREA. THE BREAKS IN THE CLOUDINESS COULD PERSIST INTO THE EARLY AFTERNOON BEFORE BEING OVERWHELMED BY THE INCREASING AMOUNTS OF MOISTURE STREAMING INTO THE REGION. WHILE MOISTURE IS INCREASING AND SPOTTY LIGHT RAIN OR SPRINKLES ARE POSSIBLE NEAR THE SC BORDER AND ACROSS THE SOUTHWESTERN AND WESTERN PIEDMONT LATER THIS AFTERNOON...TODAY WONT BE A WASHOUT. THE MORE SIGNIFICANT RAIN WILL HOLD OFF TO AROUND/AFTER SUNSET OR EVEN MORE SO OVERNIGHT TONIGHT. PROXIMITY RAOBS THIS MORNING NOTE A STILL SOMEWHAT DRY LOWER THIRD OF THE TROPOSPHERE WHICH SHOULD HOLD OF MUCH IN THE WAY OF MEASURABLE RAIN FOR MANY MORE HOURS. GUIDANCE AND RADAR TRENDS ARE CONSISTENT IN THIS PICTURE AND HAVE ADJUSTED POPS FOR TODAY SLIGHTLY DOWNWARD TO THE SLIGHT CHANCE RANGE. SOME BREAKS IN THE CLOUDS AND THE LIMITED PRECIP SHOULD ALLOW TEMPS TO CREEP UP A BIT. HAVE ADJUSTED HIGHS UPWARD A DEGREE OR TWO WITH HIGHS IN THE 50-58 RANGE. -BLAES && .SHORT TERM /TONIGHT THROUGH SUNDAY/... AS OF 255 AM FRIDAY... FOR TONIGHT: THE MID LEVEL SHORTWAVE TROUGH OVER THE DESERT SW AND ADJACENT MEXICO WILL HEAD EAST... WHILE AT THE SURFACE... LOW PRESSURE WILL TRACK UP THE LOWER MISS VALLEY AS THE ATTENDING WARM FRONT EXTENDING EAST OF THE LOW ACROSS THE GULF STATES APPROACHES NC. THE WEAK HIGH OVER THE REGION TODAY WILL DRIFT NORTHWARD... MERGING WITH POLAR HIGH PRESSURE OVERNIGHT... CULMINATING IN A STRONG (1038-1040 MB) HIGH CENTERED OVER SW QUEBEC WEDGING DOWN THE EASTERN SLOPES INTO CENTRAL NC BY SUN MORNING. THE COLUMN OVER CENTRAL NC WILL STEADILY MOISTEN TO THE POINT OF DEEP SATURATION AREAWIDE... FOSTERED BY HIGH-PW ADVECTION (TO NEARLY 250% OF NORMAL)... DEEPENING MOIST ISENTROPIC UPGLIDE... AND IMPROVING LOW LEVEL MOISTURE TRANSPORT. WEAK BUT PERSISTENT UPPER DIVERGENCE SHOULD ALSO STRENGTHEN DEEP-LAYER LIFT... ALTHOUGH THE ABSENCE OF OTHER STRONG DYNAMICS TONIGHT WILL LIMIT AMOUNTS SOMEWHAT. NEVERTHELESS... MOST OF CENTRAL NC SHOULD SEE AT LEAST SOME MEASURABLE AMOUNTS OF RAIN... AND WILL CONTINUE THE TREND OF POPS UP TO LIKELY FROM SW TO NE OVERNIGHT. WEAK COOL AIR ADVECTION WILL DEVELOP LATE AS LIGHT/VARIABLE SURFACE WINDS BECOME MORE UNIFORMLY FROM THE NE AND ENE AS THE HIGH WEDGES SOUTHWARD INTO THE AREA. EXPECT TEMPS TO FALL OFF IN THE EVENING THEN HOLD STEADY OVERNIGHT... LEADING TO LOWS FROM THE UPPER 30S TO LOWER 40S. FOR SAT/SAT NIGHT: THE MID LEVEL TROUGH OVER THE CENTRAL CONUS CONTINUES TO PUSH SLOWLY EASTWARD TOWARD NC... AS THE CHILLY SURFACE RIDGE WEDGES INTO CENTRAL NC. MODELS DEPICT THE WARM FRONT PUSHING INTO SE NC BY SAT MORNING... THEN TRACKING NNW INTO THE PIEDMONT BY SAT EVENING... AND NW OF THE FORECAST AREA BY DAYBREAK SUN... AS THE PRIMARY SURFACE LOW INTENSIFIES WHILE TRACKING FROM SRN ARK TO MI... WITH A TRAILING COLD FRONT SHIFTING INTO THE TN VALLEY. WHILE WE ARE LACKING STRONG DYNAMIC FORCING FOR ASCENT (BEST UPPER DIVERGENCE IS WELL TO OUR NORTH AND WEST NEARER THE INTENSIFYING SWRLY UPPER JET OVER THE MID MISS AND OH VALLEY... AND THE BUILDING RIDGE OVER THE EAST COAST AHEAD OF THE TROUGH WILL LIMIT DPVA)... THE INFLUX OF HIGH PW AND DEEPENING MOIST UPGLIDE PARTICULARLY IN THE 290-300K LAYER JUSTIFIES HIGH POPS... HIGHEST OVER THE NORTH/WEST WHERE THE OVERRUNNING IS APT TO BE STRONGEST OVER THE DEEPEST PART OF THE COLD DOME. WILL RETAIN THE EXISTING 50-60% POPS FOR SAT WITH SLIGHTLY LOWER CHANCE POPS SAT NIGHT. THE LACK OF STRONG DYNAMICS SHOULD CONTINUE TO LIMIT QPF... ESPECIALLY HEADING INTO SAT NIGHT AS THE MOIST UPGLIDE WANES. AS IS TYPICAL IN DAMMING SCENARIOS... TEMPS WILL BE A CHALLENGE. THE PARENT HIGH IS INDEED QUITE STRONG WITH A TAP OF COLD AIR AVAILABLE TO CENTRAL NC TO REINFORCE THE WEDGE REGIME... BUT IT IS ALSO RATHER PROGRESSIVE... MOVING STEADILY INTO THE MARITIMES THROUGH SAT NIGHT. FOLLOWING CLIMATOLOGY FOR SUCH EVENTS WITH A NOD TO MODELS` THERMAL FIELDS... EXPECT TEMPS TO RISE ONLY A FEW DEGREES IN THE NW CWA SAT BUT WE SHOULD SEE A GREATER RISE IN THE SE... INTO THE MID-UPPER 50S AS THE WARM FRONT EASES INTO THE SE CWA. MODELS CONTINUE TO INDICATE AN INLAND SURGE OF THE WEDGE WARM FRONT THROUGH MOST IF NOT ALL OF CENTRAL NC SAT NIGHT... SUPPORTING TEMPS RISING THROUGH THE 50S TO AROUND 60 OVERNIGHT... ALTHOUGH CLIMATOLOGY DICTATES THAT WE SHOULD RETAIN A SLIVER OF THE WEDGE REGIME OVER THE EXTREME NW CWA THROUGH SAT NIGHT... AS THE STRONG WARM AIR ADVECTION JUST ALOFT (925-850 MB) REINFORCES THE SURFACE-BASED STABLE AIR VIA VERTICAL DIFFERENTIAL TEMP ADVECTION. THIS ALL BOILS DOWN TO HIGHS OF 43-56 SAT... LITTLE TO NO CHANGE FROM EARLIER FORECASTS... WITH THE SAME READINGS FOR LOWS SAT NIGHT AS TEMPS RISE OVERNIGHT. WE MAY SEE SUBSTANTIAL FOG FORM... ESPECIALLY WITHIN THE WEAKENING WEDGE AIR MASS. FOR SUN: THE PRIMARY SURFACE LOW WILL MOVE NE THROUGH SE ONTARIO AND SW QUEBEC ON SUNDAY... AS THE TRAILING COLD FRONT APPROACHES CENTRAL NC... PUSHING SLOWLY THROUGH THE FORECAST AREA IN THE VERY LATE AFTERNOON THROUGH EARLY EVENING. CENTRAL NC SHOULD BE FIRMLY INTO THE WARM SECTOR SUNDAY... AND WITH THE BEST MOIST ISENTROPIC UPGLIDE HAVING SHIFTED TO OUR NW... WE SHOULD BE LEFT WITH PLENTY OF MOISTURE BUT FEW MECHANISMS TO FORCE ASCENT UNTIL THE FRONT MOVES THROUGH. WILL CONTINUE SAT NIGHT`S RELATIVE LULL IN PRECIP... WITH A CHANCE OF PATCHY LIGHT SHOWERS IN THE MORNING... FOLLOWED BY LIKELY POPS AREAWIDE BY MID-AFTERNOON SUNDAY AS THE FRONT MOVES IN. MODELS CONTINUE TO SHOW MUCAPE VALUES OF AS MUCH AS 250-500 J/KG AHEAD OF THE FRONT WITH DEEP LAYER SHEAR NEAR 50 KTS... AND GIVEN THE STRONG AND VEERING LOW LEVEL WIND FIELD... A STRONG STORM OR TWO IS NOT OUT OF THE QUESTION. EVEN OUTSIDE OF ANY STORMS... BLUSTERY AND GUSTY SW WINDS ARE LIKELY... PARTICULARLY IF WE CAN ACHIEVE GOOD LOW LEVEL MIXING. MODELS CONTINUE TO TREND WARMER ACROSS THE BOARD FOR SUNDAY... AND WHILE THIS WARMTH WILL LIKELY BE MUTED OVER THE FAR NW PIEDMONT... WILL LEAN TOWARD THIS TREND AND RAISE HIGHS A BIT... TO MILD READINGS FROM THE MID 60S TO MID 70S. -GIH && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... AS OF 255 AM FRIDAY... A COLD FRONT PUSHES EAST AND OUT OF THE STATE SUNDAY NIGHT...WITH THE GFS SLIGHTLY FASTER THAN THE ECMWF IN THE TIMING OF THE FRONTAL PASSAGE. THE CURRENT FORECAST OF HIGHER CHANCES FOR SHOWERS MAINLY SUNDAY EVENING AND GRADUATED WEST-TO-EAST SEEMS SOUND AND HAVE CONTINUED THIS...WHILE ALSO MAINTAINING A CHANCE OF EVENING THUNDER MAINLY ALONG AND EAST OF U.S. 1 SUNDAY EVENING. GFS LIFTED INDICES ARE -1C TO -3C AND ITS 0-3KM SHEAR IS GREATEST WITH THE FRONTAL PASSAGE...WHILE THE ECMWF LIFTED INDICES ACTUALLY INCREASE IN TEMPERATURE OR BECOME MORE STABLE AS THE FRONT MOVES EAST WITH ITS BEST 0-3KM SHEAR LAGGING THE FRONT. 1000-500MB LAPSE RATES ARE FORECAST JUST BELOW 6C/KM...WHICH FOR WINTER PROBABLY IS NOT TOO BAD...AND 850MB WINDS ARE FORECAST AROUND 50KT COINCIDENT WITH THE SURFACE FRONT. DUE TO TIMING AND INSTABILITY UNCERTAINTIES WILL LEAVE THE MENTION OF ANY STRONG STORMS OUT OF THE HWO FOR THIS FORECAST...NOTING A GUSTY WIND WITH A MORE INTENSE SHOWER OR A THUNDERSTORM IS POSSIBLE MAINLY EAST OF U.S. 1 SUNDAY EVENING. BEYOND SUNDAY NIGHT...SURFACE HIGH PRESSURE EXTENDS ACROSS THE GULF THROUGH MUCH IF NOT ALL OF THE REST OF THE LONG-TERM PERIOD...WHICH SHOULD CERTAINLY LIMIT LOW-LEVEL MOISTURE RETURN TOWARD CENTRAL NORTH CAROLINA. ANOTHER SURFACE FRONT SHOULD MOVE ACROSS CENTRAL NORTH CAROLINA LATE TUESDAY INTO EARLY WEDNESDAY...AND WHILE THIS FRONT SHOULD MOVE THROUGH DRY...IT SHOULD YIELD QUITE CHILLY TEMPERATURES FOR THE END OF THE WEEK...COLDEST THURSDAY WITH HIGHS IN MANY LOCATIONS LIKELY STAYING IN THE 30S. AN UPPER-LEVEL TROUGH AXIS MOVES THROUGH THE MID-ATLANTIC AND CENTRAL NORTH CAROLINA LATE WEDNESDAY INTO THURSDAY...AND AHEAD OF THIS TROUGH AXIS THERE IS FORECAST AN INCREASE IN MID-LEVEL MOISTURE OVER THE AREA FOR WEDNESDAY. MODEL QPF IS NONE AND MEX AND MEE MOS GUIDANCE POPS ARE BELOW CLIMATOLOGY...SO WILL LEAVE THE FORECAST DRY FOR NOW. A FORECAST ALTERNATIVE WOULD BE VERY LIGHT AND MOSTLY TRACE PRECIPITATION TOWARD THE VIRGINIA BORDER WHERE THE DRY 850MB AIR IS NOT QUITE AS DRY RELATIVE TO THE REST OF CENTRAL NORTH CAROLINA. SPEAKING OF DRY AIR...WITH THE COLDER AIR COULD COME SOME FAIRLY LOW SURFACE DEW POINTS. SOME GUIDANCE SUGGESTS SURFACE DEW POINTS WELL BELOW ZERO THURSDAY...POSSIBLY CLOSE TO -10F BY THURSDAY AFTERNOON. WILL HOLD OFF GOING THAT LOW FOR NOW...BUT STILL SHOW WIDESPREAD SURFACE DEW POINTS OF ZERO TO -5F THURSDAY. 1000-850MB THICKNESSES WOULD SUPPORT LOWS THURSDAY NIGHT BELOW THE FORECAST...BUT WILL STRAY CLOSER TO THE HPC AND MOS GUIDANCE...STILL FORECASTING A LOT OF TEENS...OVER CONCERNS ABOUT UPPER-LEVEL MOISTURE IN THE NORTHWEST FLOW ALOFT AND POSSIBLY DUE TO OROGRAPHIC EFFECTS. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... AS OF 640 AM FRIDAY... PRIMARY AVIATION CONCERN: A TREND TOWARD MVFR CIGS FROM SW TO NE STARTING LATE THIS AFTERNOON... AND TO IFR/LIFR CIGS AND MVFR VSBYS TONIGHT. LOW PRESSURE DEVELOPING JUST OFF THE TX GULF COAST HAS A WARM FRONT EXTENDING EASTWARD ALONG THE GULF COAST. THIS LOW WILL STRENGTHEN AND TRACK NE THROUGH THE LOWER MISS VALLEY TOWARD MICH TODAY AND TONIGHT... AS THE WARM FRONT TRACKS NORTHWARD TOWARD NC. VFR CLOUDS WILL CONTINUE TO SPREAD IN FROM THE WEST AND STEADILY THICKEN AND LOWER OVER CENTRAL NC THROUGH TODAY... BUT CIGS ARE EXPECTED TO REMAIN VFR THROUGH AT LEAST 21Z. CIGS SHOULD THEN SLOWLY LOWER TO MVFR BETWEEN 22Z AND 02Z... FIRST AFFECTING INT/GSO/FAY THEN RDU/RWI. MVFR CIGS SHOULD THEN DOMINATE AT ALL SITES AFTER 02Z THROUGH THE END OF THE TAF VALID PERIOD... WITH PATCHY LIGHT RAIN MOVING IN... ALTHOUGH VFR VSBYS SHOULD REMAIN DOMINANT INITIALLY. AFTER ABOUT 05Z-07Z... CIGS WILL CONTINUE TO TREND DOWNWARD... TO IFR/LIFR OVERNIGHT AT ALL SITES... WITH RAIN BECOMING MORE WIDESPREAD YIELDING MVFR VSBYS. WINDS WILL STAY LIGHT AND VARIABLE WITH SPEEDS MAINLY UNDER 5 KTS... BECOMING PREDOMINANTLY FROM THE ENE AFTER 00Z. LOOKING BEYOND 12Z SAT MORNING... STARTING BY DAYBREAK SAT AND CONTINUING SAT THROUGH SAT NIGHT... EXPECT IFR/LIFR CIGS AND MVFR/IFR VSBYS WITH PERIODS OF LIGHT RAIN AND DRIZZLE AT ALL SITES. THE CRITERIA OF LOW LEVEL WIND SHEAR ARE UNLIKELY TO BE MET INITIALLY... ALTHOUGH WE WILL STILL SEE STRENGTHENING AND VEERING WINDS WITH HEIGHT LATE TONIGHT THROUGH SAT. BY SUNSET SAT THE CHANCE OF LLWS WILL INCREASE AND REMAIN HIGH THROUGH SAT NIGHT... UNTIL THE WARM FRONT TRACKS TO THE N OR NW THROUGH THE AREA. SUB-VFR CIGS WILL HOLD INTO SUN... WITH A GOOD CHANCE OF SHOWERS AND FEW STORMS AHEAD OF A COLD FRONT THAT WILL SWEEP EAST THROUGH THE AREA SUN AFTERNOON/EVENING. VFR CONDITIONS WILL RESUME POST-FRONT SUN NIGHT THROUGH TUE AS HIGH PRESSURE BUILDS INTO THE AREA. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. &&
Posted on: Fri, 02 Jan 2015 16:48:25 +0000
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